was having po171 and p0174 but i repaired some vacuum lines but still had the codes then changed fuel filter and both codes went away for 300 to 400 miles but now i am getting the po171 code only.i have a 2002 supercrew 5.4 with a lighting supercharger on it.i am wondering if i could have a leak on the intake or bad injector? when i put in the spark plugs i was told to gap at .39 and was wondering if that could also be a problem.going to check fuel presure saturday.any help would be great.

 

My first response while reading the post was intake leak but don't over look a exhaust leak too. How long have you had the supercharger on?

 

I had the same problem on and off for a cpl of months. Tha last 2 things I did was replace the PCV assembly (I read on this forum that the rubber boot that connects to the TB can go bad and leak and cause this code), OEM from Ford for $28.00 and cleaned my MAF sensor one more time with CRC electronics cleaner. My code hasn't come back in months.
Funny thing was, my truck was running great when I got the same problem as you and it runs great now. The CEL just kicked on one day and it drove me nuts checking everything. Then I did the above and all is good.
It might be a good idea to ck your vacuum pressure w/ a gauge, I did to eliminate that cause. If it was an injector, I think you would be throwing another code but there are others on this forum that could answer that better.

Good Luck !

TJK

 

i have had the supercharger on for about 40000 miles or 2 1/2 years